Methods and Apparatus for Credit-Based Flow Control

1. A method comprising: receiving a plurality of frames at a fibre channel switch from a first network node; forwarding the plurality of frames; modifying credit information associated with the first network node based on the number of frames forwarded; and providing an extended receiver ready signal including the credit information to the first network node, the extended receiver ready signal including the credit information indicating to the first network node that a plurality of buffers are available to receive transmissions from the first network node, wherein the first network node does not send a frame to the fibre channel switch unless the first network node has a credit available, wherein the first network node further maintains a credit value indicating the number of buffers available to receive transmissions from the first network node, a credit difference calculated by subtracting a last buffer advertisement from a current buffer advertisement received from the fibre channel switch and adding the credit difference to the credit value.

2. The method of claim 1 , wherein the extended receiver ready signal further includes priority information.

3. The method of claim 2 , wherein the priority information is used to differentiate amongst eight levels of priority.

4. The method of claim 1 , further comprising providing an initialization extended receiver ready signal to the first network node before receiving the plurality of frames.

5. The method of claim 4 , wherein the initialization extended receiver ready signal includes initialization credit information.

6. The method of claim 4 , wherein the initialization credit information is a buffer advertisement for determining an initial number of credits available to the first network node.

7. The method of claim 6 , wherein each credit allows the first network node to transmit a single frame.

8. The method of claim 5 , wherein the initialization credit information is a buffer advertisement for determining an initial number of buffers available for receipt of frames from a first network node.

9. The method of claim 1 , wherein the credit information is a buffer advertisement for determining a relative number of credits available to the first network node.

10. The method of claim 9 , wherein the credit information is a buffer advertisement for determining a relative number of buffers available for receipt of frames from a first network node.

11. The method of claim 10 , wherein the fibre channel switch maintains the last buffer advertisement provided to the first network node.

12. The method of claim 10 , wherein the first network node maintains the last buffer advertisement received from the fibre channel switch.

13. The method of claim 8 , wherein each buffer is configured to hold a single frame.

14. The method of claim 1 , wherein the extended receiver ready signal further comprises an error detection code.

15. The method of claim 1 , wherein the extended receiver ready signal is an ordered set.

16. The method of claim 15 , wherein the extended receiver ready signal is transmitted after two idle ordered sets are transmitted.

17. A network node the network node comprising: an output interface operable to transmit a plurality of frames to a fibre channel switch; an input interface operable to receive an extended ready signal from the fibre channel switch, the extended ready signal including credit information; a processor coupled to the input interface and the output interface, the processor configured to use the credit information to determine the number of buffers available to receive transmissions from the network node; a memory operable to maintain a credit value indicating the number of buffers available to receive transmissions from the network node, a credit difference calculated by subtracting a last buffer advertisement from a current buffer advertisement received from the fibre channel switch and adding the credit difference to the credit value has been added.

18. The network node of claim 17 , wherein the extended receiver ready signal further includes priority information.

19. The network node of claim 18 , wherein the priority information is used to differentiate amongst eight levels of priority.

20. The network node of claim 17 , wherein the input interface is further configured to receive an initialization extended receiver ready signal from the fibre channel switch before sending the plurality of frames.

21. The network node of claim 20 , wherein the initialization extended receiver ready signal includes initialization credit information.

22. The network node of claim 20 , wherein the initialization credit information is a buffer advertisement indicating an initial number of credits available to the network node.

23. The network node of claim 22 , wherein each credit allows the network node to transmit a single frame.

24. The network node of claim 21 , wherein the initialization credit information is a buffer advertisement for determining an initial number of buffers available for receipt of frames from a network node.

25. The network node of claim 17 , wherein the credit information is a buffer advertisement for determining a relative number of credits available to the network node.

26. The network node of claim 25 , wherein the credit information is a buffer advertisement for determining a relative number of buffers available for receipt of frames from a network node.

27. The network node of claim 26 , wherein the fibre channel switch maintains the last buffer advertisement provided to the network node.

28. The network node of claim 26 , wherein the network node maintains the last buffer advertisement received from the fibre channel switch.

29. The network node of claim 24 , wherein each buffer is configured to hold a single frame.

30. The network node of claim 17 , wherein the extended ready signal further comprises an error detection code.

31. The network node of claim 17 , wherein the extended ready signal is an ordered set.

32. The network node of claim 31 , wherein the extended ready signal is transmitted after two idle ordered sets are transmitted.

33. A system, comprising: means for receiving a plurality of frames at a fibre channel switch from a first network node; means for forwarding the plurality of frames; means for modifying credit information associated with the first network node based on the number of frames forwarded; and means for providing an extended receiver ready signal including the credit information to the first network node, the extended receiver ready signal including the credit information indicating to the first network node that a plurality of buffers are available to receive transmissions from the first network node, wherein the first network node does not send a frame to the fibre channel switch unless the first network node has a credit available, wherein the first network node further maintains a credit value indicating the number of buffers available to receive transmissions from the first network node, a credit difference calculated by subtracting a last buffer advertisement from a current buffer advertisement received from the fibre channel switch and adding the credit difference to the credit value.